I can recommend Maribor - and the Pohorje mountains. Breathtaking roads into fairy tale forests. Since you're going out of season, you can stay in the luxury hotels for incredibly cheap prices. I stayed in the (four star) Bellevue - and got dinner and breakfast AND spa treatments for £40 per night.
There is a fantastic place to eat in the mountains called Gostice Katarina - local, traditional food, at amazing prices.
Follow the road from Maribor along the Drava river towards Dravograd - its like being transported to a magical world of chocolate box cottages and misty mountains.
This is also the wine route. Look up Limbus - there is a restaurant Gostisce Vnukec - who will not only educate and serve you local dishes, but also wine from the region and advise you on which wineries to visit.
At the foot of the Pohorje is a coffee shop, called Kavarna Pohorje - if you love gorgeous GORGEOUS coffee and hot chocolate - you will think you had died and gone to heaven. (Their hot chocolate is so thick, you can almost eat it with a spoon, and they have about 30 varieties!)
Here's some pics I took on my last visit. (which incidentally was September - in my opinion the most beautiful time to visit)